The present invention is related to a system for mounting a control circuit in an image reading apparatus.
Generally, image reading apparatus such as image scanners and facsimile machines are known as input apparatus of digital images. Since computers require high performance, image reading apparatus require high-speed performance. For instance, image reading apparatus may be operated in high speeds in such a manner that widths of control signals, such as a shift pulse and a reset pulse used to control CCDs (charge-coupled devices) which is widely employed as elements for converting optical information into electronic information, are set to short pulse widths of high-frequency control signals, and widths of sampling signals for A/D converters are set to short pulse widths of high-frequency sampling signals.
FIG. 5 shows a related flat bed type image scanner, in which both a CCD 22 and an A/D converter 25 are provided in a carriage 20, an image processing ASIC 52 including a control circuit 51 is provided in a case 11 for supporting the carriage 20, and the control circuit 51 generates a control signal used for the CCD 22 and a sampling signal used for the A/D converter 25. The image processing ASIC 52, the CCD 22, and the A/D converter 25 are connected to each other by employing a flexible flat cable 53 (will be referred to as an “FFC” hereinafter) having a length of several tens cm. That is, in the related flat bed type image scanner, the transmission path for the above-explained control signals and the like is very long. As a result, although an EMI (ElectroMagnetic Interference) measure should be sufficiently introduced in the vicinity of the FFC 53, due to the long length of the transmission path, distortion of waveforms of signal occurs and timing of the signal delays. In addition, the distortion of waveforms of signals occurs and timing of the signal delays due to the employment of such an EMI measure which employs a filter, a resistor, etc. To prevent these drawbacks, high cost components are necessary for the EMI measure. Therefore, this EMI measure may conduct cost-up matters of final products.
Furthermore, when the related flat bed type scanner is operated in a high speed by generating a clock signal having a higher frequency, or a pulse signal having a shorter pulse width, there is such a problem that since distortion of waveforms of signal occurs and timing of the signal delays due to an EMI filter and a resistor, frequencies of signals cannot be set to considerably high frequencies. Accordingly, in such a related flat bed type image scanner, both the width of the control signal for the CCD 22 and the pulse width of the sampling signal for the A/D converter 25 are set to be on the order of 40 nsec. In image reading apparatus such as flat bed type image scanners, both EMI measures and also lengths of signal transmission paths may constitute barriers for high-speed operations thereof in view of mounting techniques.